In magnetic recording, an electrical current signal is converted to a corresponding induced magnetization in a magnetic medium, e.g., tape or disk. This is done with a transducer, commonly referred to as a head, which transforms the electrical signal into a magnetic field which influences the recording medium as it is transported near the head. A magnetic remanence representative of the field is left in the medium. In the playback, or reproduce mode, the magnetic flux from the medium links through, or modulates, the magnetic circuit of the playback head and induces a voltage change in the head winding. This measured or detected voltage change is subsequently amplified.
Although the thickness of the recording layer on a recording medium is rather small (e.g., 0.1 to 10 micrometers) it is generally only that portion of the layer nearest the head which provides most of the total flux.
Recent advances in the field of magnetic recording have been directed toward high density recording which is especially valuable in the fields of video, instrumentation and data recording. In perpendicular recording, which is felt to be advantageous for high density recording, the easy axis of magnetization of the recording medium is perpendicular to the plane of the medium itself, and the remanence imposed in the medium is a perpendicular remanence.
U.S. Pat. No. 4,210,946 describes a recording medium specifically designed for perpendicular or vertical recording. This medium has a layer of low coercive force material interposed between the magnetic recording layer and the non-magnetic base which supports both the magnetic recording layer and the low coercive force material layer. The advantages of this low coercive force material under-layer are said to be that: (a) it appears to enhance the magnetic field produced by a single-pole magnetic head; and (b) it forms a partially closed magnetic circuit so as to reduce the demagnetization field of the magnetic recording layer.
A pole head differs from the conventional ring head in that it does not have a gap between two poles which gap is used to generate a stray magnetic field. Instead, a pole head comprises a magnetic core and a signal coil usually wrapped around the core. The state of the art in pole head design varies in the placement of auxiliary poles (see U.S. Pat. No. 4,210,946, Column 2 and FIG. 6) and return flux poles, and in the size and placement of the writing pole or core in relation to the auxiliary poles and the current winding. The writing pole is generally oriented normal to the medium. The use of pole heads in vertical recording is discussed in Middleton, B.K. and Wright, C.D., "Perpendicular Recording", presented at the 4th International Conference on Video and Data Recording sponsored by the Institution of Electronic and Radio Engineers, in Great Britain, Apr. 20-23, 1982.
According to present theories, an increase in head field gradient will allow an increase in recorded data density. Therefore, the vertical magnetic field intensity decrease as a function of distance away from the trailing edge (i.e. the last part of the head which influences the magnetic recording medium) should be rapid. Conversely, as referred to herein, the leading edge of a head is the first part of the head which influences the tape or medium by its magnetic field.